Props, supporting girders and boards forming the formwork surface of the floor slab are basically involved in two-way floor slab or flat floor slab typologies, which are extensively used in Spain. In the assembly of the formwork, several alignments of supporting girders arranged parallel to one another and supported on props and additionally on the side faces of some of the already concreted pillars are first placed. Then, the girders are placed in a direction perpendicular to the alignments of the supporting girders, fitting and being supported in the housings of the upper face of the supporting girders which are separated from one another by a fixed inter-axis distance. Finally, the boards are placed, supporting them on the mentioned girders.
These meccano systems are generally suitable for the formwork of open spaces, in which the formwork may remain in a cantilever way. In contrast, when the floor slab formwork is surrounded by walls, it is very complicated to adjust the girders and the supporting girders against said walls, the meccano assembly falling too short, which generally forces finishing the formwork with wooden planks, going against the industrialization of the meccano system, the formwork process becoming a slow and laborious task.
Spanish patent ES2244282 solves the aforementioned problem by providing a supporting girder having spaces for fitting girders in multiple groups of adjacent and identical housings, particularly groups of three, distributed along the upper face of the supporting girders. Said arrangement makes it possible, upon reaching an area having an opening with a length smaller than that of a girder, to arrange, next to each of the girders placed until that time, which are supported at their ends on the supporting girders, another new girder housed in one of the housings adjacent to the already placed girders. The new girder which will cover the opening can thus run through the mentioned housing of the same group in order to achieve the sufficient and suitable free length for covering the remaining opening. The useful length of the new girder may be adjusted to the one needed in each case, since the supporting girder lacks longitudinal stops.
Furthermore, the longitudinal extension of the supporting girders has also been provided since they are provided, close to one of their ends, with a lower flange having a hole, on each side of the supporting girder, suitable for receiving the lower centering rod of another supporting girder which will be used as an extension of the previous one. The overlap length between supporting girders is obviously conditioned by the alignment which there must be between the housings of both elements.
Despite the fact that the supporting girder described above has considerable advantages in terms of the extension of the girders for covering the surface to be formed, while carrying out a construction work it is usual that reconsiderations happen and therefore, the position and/or dimensions of elements such as stairwells, elevator shafts, conduit passage gaps, etc. have to be changed, having to resort again to improvised solutions since neither the number nor the position of the girders fitted in the corresponding housings of the supporting girders can be changed.
Furthermore, the fixed position occupied by the groups of three housings restricts the possibilities of extension by the overlapping the supporting girders since the transverse alignment between said groups has to be ensured for such purpose, which forces providing the supporting girder with at least one lower centering rod and with a lower flange provided with a hole on each side of the supporting girder for receiving the rod of another supporting girder. For example, if the supporting girders have five groups of three housings distributed equidistantly to one another, they are provided with a sole lower flange arranged under the central housing of a group of three located at one of the ends of the supporting girder, and with a single centering rod arranged under the central housing of the group located at the middle of the length of the supporting girder, a supporting girder can only be extended a distance equivalent to half its length since when the centering rod of a supporting girder is inserted in the hole of the flange of another one, the overlap length will be half the length of a supporting girder.
Therefore, the need to have a more versatile supporting girder with which the whole surface to be formed can be covered, which can easily be adapted to several types of boards, and to the requirements of loads and deflections of the floor slabs depending on which a larger or smaller number of supporting girder is placed.